Heat exchanger

ABSTRACT

The heat exchanger has an axis and at least one heat-exchange body ( 5 ) encompassing said axis, annular in cross-section and comprising sheet metal elements ( 23, 27 ) which are present in succession around the axis and are involute in cross-section and between which edge strips ( 24, 25, 28, 29 ) welded to said sheet metal elements alternately at their involute side edges ( 23   c,    23   d,    27   c,    27   d ) and at their inner and outer edges ( 23   a,    23   b,    27   a,    27   b ) are arranged and which alternately bound passages ( 33, 34 ) for a first and a second fluid ( 15, 16 ). Each passage ( 33, 34 ) contains an intermediate layer ( 31, 32 ) which consists of a knitted wire fabric. The edge strips ( 24, 25, 28, 29 ) and the knitted wire fabrics hold the successive sheet metal elements ( 23, 27 ) in a stable and durable manner a distance apart and result in only little thermal conduction in the direction of flow.

FIELD OF THE INVENTION

[0001] The invention relates to a heat exchanger comprising at least oneheat-exchange body having successive sheet metal elements which,together with gas-permeable intermediate layers arranged between them,alternately bound passages for a first fluid and a second fluid.

[0002] The heat exchanger is provided in particular for transferringheat between two gaseous fluids. The heat exchanger can be used, forexample, for recovering heat from hot exhaust gas of a hot gas engine,such as a Stirling engine or a gas turbine, and transferring it tooriginally cold air which is heated by the heat transfer and is then fedto a burner.

PRIOR ART

[0003] A heat exchanger disclosed in GB 892 962 A has a heat-exchangebody which is annular in cross-section and comprises sheet metalelements. These have a middle section with the shape of an Archimedeanscrew and with wavy ribs which run along said section and evidently restagainst an adjacent sheet metal element and keep the ribless regions ofthe middle sections a distance apart so that they bound spiral passages.The inner and outer edge sections of the sheet metal elements aremultiply angled or curved so that they rest against one another at theinnermost or outermost part-sections and bound axial channels. The sheetmetal elements are connected to one another by welding or soldering.Rings which alternately close the axial channels present in successionalong the circumference or connect said channels to an adjacent space bymeans of a hole are fastened at the two ends of the heat-exchange body.During operation of the heat exchanger, hot exhaust gas is passed fromthe inside to the outside and cold air is passed from the outside to theinside through the heat-exchange body.

[0004] The exhaust gases flowing out of a Stirling engine or a gasturbine have, in the case of modern engines or gas turbines, hightemperatures which are frequently 500° C. to about 1000° C. or evenslightly higher. If such exhaust gas is fed to a heat-exchange body, itssheet metal elements are subjected to large temperature changes at thebeginning and at the end of operation of the heat exchange. Furthermore,considerable temperature gradients occur along the flow paths of thefluids in a heat-exchange body with through-flow during operation. Suchtemperature changes cause changes in dimensions, which differ from placeto place owing to the temperature gradients.

[0005] Sheet metal elements according to GB 892 962 A which are providedwith ribs and are multiply angled or curved at the inner edges and outeredges can be highly and permanently deformed by the dimensional changesoccurring at high exhaust gas temperatures and the stresses associatedtherewith. The deformations are further increased by the fact that thecurved edge sections of the sheet metal elements, which sections areadjacent to one another, connect all sheet metal elements relativelyrigidly and inflexibly to one another. The deformations produced in turnhave the result that the passages are widened in parts and narrowed inparts or even more or less completely closed, with the result that theproperties of the heat exchanger are very adversely affected. Moreover,GB 892 962 A does not reveal whether and how the spiral passages at thetwo ends of the heat-exchange body are closed and whether and how mixingof the hot exhaust gas with the air can be prevented there and at theaxial channels of the heat-exchange body. Owing to the complicatedshapes of the sheet metal elements, because the rings mentioned musthave a hole flush with the channel for every second axial channel andbecause the inner ends of the spiral middle sections of the sheet metalelements make, in a section perpendicular to the axis, a fairly acuteangle with the inner lateral surface of the heat-exchange body, thelatter—in the case of a specific, given internal diameter, can moreoverhave only a relatively small number of passages distributed around itsinner lateral surface. Furthermore, the production of the curved edgesections is complicated and expensive.

[0006] U.S. Pat. No. 4,506,502 A discloses a heat exchanger comprisingan annular heat-exchange body having spiral passages. The heat-exchangebody consists of ceramic or steel, but the internal structure and theproduction of the heat-exchange body are not disclosed in more detail.In addition, the hot exhaust gas is passed from the outside to theinside through the heat-exchange body during operation. Theheat-exchange body therefore becomes very hot at its outer lateralsurface, so that a great deal of heat is released to the environment andhigh heat losses occur.

[0007] The heat exchanger disclosed in U.S. Pat. No. 3,741,293 A has anannular heat-exchange body with flat, radial sheet metal elements andsecondary surface elements which are arranged in rows in between and areformed by peeling. Since the passages are radial, they become broadertoward the outside and have only a small length. In addition, thedistance between the adjacent sheet metal elements is relatively large.This heat-exchange body therefore gives only a low heat-exchangeperformance based on a specific volume. Moreover, this heat exchangeralso has some disadvantages similar to the heat exchanger according tothe first-cited GB 892 962 A.

[0008] A heat exchanger disclosed in U.S. Pat. No. 5,060,721 A has anannular heat-exchange body with in general involute sheet metalelements. Each of these forms an irregular hexagon in the unwound, flatstate and has a trapezoidal middle section and a wing on both sides ofthis. The middle section has waves running along the involutes. Thewings have in part waves which form channels approximately parallel tothe axis of the heat-exchange body. This heat exchanger has somedisadvantages similar to the heat exchanger according to GB 892 962 A,in particular the production and the assembly of complicated sheet metalelements being time-consuming and expensive.

[0009] GB 1 172 247 A discloses heat exchangers comprising anapproximately right parallelepiped heat-exchange body. This has a stackof rectangular plates with a flat main section and edge sections bentupward. An intermediate layer consisting of a wire lattice is arrangedbetween the adjacent plates. In the case of the variants shown in thedifferent figures of the drawings, the wire lattices consist of wiresresting one on top of the other and intersecting one another at rightangles. According to the figures, said wires make angles of about 45°with the rectangular sides of the plates. When the heat exchanger isused, the fluids flowing through it generally have directions of flowwhich are more or less parallel to the longer sides of the rectangle.The wire lattices therefore result in fairly good thermal conductionalong the flow paths of the fluids. As a result of this, a large part ofthe heat supplied by the hotter fluid is transported away again fromthis out of the heat exchanger and is not transferred. Furthermore, theplates are provided at their edges with rubber seals which are notsuitable for high temperatures. These known heat exchangers wouldtherefore not be suitable for exhaust gases having temperatures up toabout 1000° C. and emitted by internal combustion engines and gasturbines.

SUMMARY OF THE INVENTION

[0010] It is the object of the invention to provide a heat exchangerwhich makes it possible to avoid disadvantages of known heat exchangers.In particular, the sheet metal elements should on the one hand beconnected to one another in a manner which is sufficiently stable anddurable so that the passages for the two fluids are and remainsatisfactorily separated from one another. On the other hand, the sheetmetal elements should retain their shapes as well as possible also whena fluid having a very high temperature is fed in and should ensure thatall passages permit uniform fluid flow. Furthermore, the heat exchangershould be capable of being produced economically and should enable theheat losses to the environment to be kept low.

[0011] This object is achieved, according to the invention, by a heatexchanger having the features of claim 1, i.e. by a heat exchangercomprising at least one heat-exchange body which is annular incross-section, encompasses an axis and has sheet metal elements whichare present in succession around said axis and together alternatelybound first passages for a first fluid and second passages for a secondfluid, each sheet metal element having an inner edge, an outer edge andtwo side edges running from the inner edge to the outer edge, adjacentsheet metal elements having substantially constant distances from oneanother along their side edges and the heat exchanger beingcharacterized in that each sheet metal element forms a quadrilateral,the [sic] metallic edge strips are arranged between the sheet metalelements together bounding a first passage and run along the side edgesof said sheet metal elements and are firmly and tightly connected to therelevant sheet metal elements and that metallic edge strips are arrangedbetween the sheet metal elements together bounding a second passage andrun along the inner edges and the outer edges of said sheet metalelements and are firmly and tightly connected to the relevant sheetmetal elements.

[0012] The invention furthermore relates to a heat exchanger comprisingat least one heat-exchange body having successive sheet metal elementswhich alternately bound passages for a first fluid and a second fluidand between which gas-permeable intermediate layers are arranged, eachsheet metal element [lacuna] two side edges facing away from one anotherand the heat exchanger being characterized in that the side edges of thesheet metal elements belonging to the same heat-exchange body and/oredge strips arranged at these side edges together define two endsurfaces of the heat-exchange body, that, at each end surface, at leastone metallic foil rests against the side edges of the sheet metalelements and that a heat insulation is arranged on that side of eachfoil which faces away from the sheet metal elements.

[0013] The invention furthermore relates to a heat exchanger comprisingat least one heat-exchange body which is annular in cross-section,encompasses an axis and has sheet metal elements which are present insuccession around said axis and together alternately bound firstpassages for a first fluid and second passages for a second fluid, eachsheet metal member having an inner edge, an outer edge and two sideedges running from the inner edge to the outer edge, adjacent sheetmetal elements having substantially constant distances from one anotheralong their side edges, the passages extending between orifices in thevicinity of the inner edges and orifices in the vicinity of the outeredges and the heat exchanger being characterized in that the sheet metalelements have a dimension, measured along their side edges, which is atleast twice the dimension of the sheet metal elements which is measuredalong the axis.

[0014] The invention also relates to a heat exchanger comprising atleast one heat-exchange body having successive sheet metal elementswhich alternately bound passages for a first fluid and a second fluidand between which gas-permeable intermediate layers are arranged, eachsheet metal element having two side edges which face away from oneanother and are parallel to one another and at least substantial partsof the passages running along the side edges and the heat exchangerbeing characterized in that each intermediate layer consists of aknitted wire fabric which has rows of stitches comprising stitchesadjacent to one another and formed from cohesive wire sections and thatthese rows of stitches are generally approximately at right angles tothe side edges of the sheet metal elements.

[0015] Advantageous embodiments of the heat exchanger are evident fromthe dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The subject of the invention is explained in more detail belowwith reference to embodiments shown in the drawings. In the drawings,

[0017]FIG. 1 shows simplified, schematic oblique view of a heatexchanger,

[0018]FIG. 2 shows a simplified, schematic axial section through theheat exchanger and its heat-exchange body,

[0019]FIG. 3 shows a schematic cross-section through the annularheat-exchange body of the heat exchanger,

[0020]FIG. 4 shows a schematic section along the line IV-IV of FIG. 3through a first involute fluid passage of the heat-exchange body,

[0021]FIG. 5 shows a section along the line V-V of FIG. 3 through asecond fluid passage of the heat-exchange body,

[0022]FIGS. 6 and 7 show views of edge sections of the unwound, secondsheet metal element shown in FIG. 5, in the directions of view indicatedin FIG. 5 by the arrows V and VI, respectively, on a larger scale,

[0023]FIG. 8 shows a view of the unwound, first sheet metal elementshown in FIG. 4, on a larger scale,

[0024]FIG. 9 shows a cut-out from FIG. 8 on an even larger scale,

[0025]FIG. 10 shows a view of the first sheet metal element shown inFIGS. 4, 8 and 9, in the direction of view indicated by X in thesefigures, on the same scale as FIG. 9,

[0026]FIG. 11 shows a simplified cross-section through a region of thatend section of the heat-exchange body which is present at the top inFIG. 2, on a larger scale than FIG. 2,

[0027]FIG. 12 shows a schematic, simplified oblique view of a region ofthe heat-exchange body with a direction of view onto the inner edge ofthe end surface present at the top in FIG. 2,

[0028]FIG. 13 shows a simplified oblique view of another, cut-away heatexchanger having only one heat-exchange body,

[0029]FIG. 14 shows a simplified plan view of the upper end of theheat-exchange body shown in FIGS. 12 and 13 and foil resting on it,

[0030]FIG. 15 shows a section along the arc XV-XV of FIG. 14 through theheat-exchange body and the foils resting on it,

[0031]FIG. 16 shows an axial section through a region of the heatexchanger according to FIG. 13 on a larger scale,

[0032]FIG. 17 shows a simplified, schematic axial section through a heatexchanger having two heat-exchange bodies,

[0033]FIGS. 18 and 19 show sections, analogous to FIGS. 4 and 5, throughthe heat-exchange body according to FIG. 17, along first and second,involute passages,

[0034]FIG. 20 shows a schematic axial section through a heat exchangerhaving six heat-exchange bodies and

[0035]FIG. 21 shows a schematic axial section through a heat exchangerhaving four heat-exchange bodies.

[0036] Regarding FIGS. 4, 5, 12 and 13, it may also be noted that thesections shown in them run along an involute passage so that the sheetmetal elements appear to be in the unwound, flat state. However, thoseparts of the housing and of the fluid conducting means which areadjacent to the heat-exchange bodies are shown in a section radial withrespect to the axis, for simplification. Moreover, it may also be notedwith regard to FIG. 12 that, for simplification, no knitted wire fabricsare shown therein. Furthermore, the sheet metal elements essentiallydistributed around an arc-shaped section of the cylindrical, innerlateral surface of the heat-exchange body are shown as if their inneredges are lying in a plane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The heat exchanger 1 shown in FIGS. 1 and 2 has an axis 2. Theheat exchanger 1 has only one housing 3 shown partly and schematically.Said housing contains a heat-exchange body 5 which is described in moredetail. The heat exchanger 1 and in particular its heat-exchange body 5are substantially rotationally symmetrical with respect to the axis 2.The heat exchanger 1 has fluid conducting means 7 which are formedpartly by housing parts and, like the housing, are shown only partly andschematically. The housing 3 and/or the fluid conducting means 7 have afirst fluid entrance 8, a first fluid exit 9, a second fluid entrance 10and a second fluid exit 11.

[0038] Furthermore, two gaseous, flowing fluids, namely a first fluid 15and a second fluid 16, are indicated by arrows in FIGS. 1 and 2. Thearrows representing the first fluid 15 are shown with solid lines andthe arrows representing the second fluid 16 are shown with dashed lines.The heat exchanger 1 may belong, for example, to an apparatus which alsohas a hot gas engine or Stirling engine which is not shown or possibly agas turbine. The engine or the turbine can then feed to the first fluidentrance 8 hot exhaust gas which forms the first fluid 15 and, afterpassing through the heat-exchange body 5, is then passed from the firstfluid exit 9, for example by an additional heat exchanger serving forthe production of hot water and/or via a filter and/or any otherapparatus, into the environment. The second fluid 16 consists, forexample, of air, which is sucked in by a suction apparatus from theenvironment and possibly compressed and fed to the second fluid entrance10. After passing through the heat-exchange body, the air is fed fromthe second fluid exit 11, for example, to a burner for operating the hotgas engine or the gas turbine.

[0039] The heat-exchange body 5 and parts thereof are shown particularlyclearly in FIGS. 3 to 12. The heat-exchange body 5 is annular incross-section and forms a ring and/or a sleeve. The heat-exchange body 5has an inner lateral surface 5 a, an outer lateral surface 5 b and twoend surfaces 5 c and 5 d facing away from one another. The two lateralsurfaces 5 a, 5 b are parallel to the axis 2 and substantiallycylindrical and are circular in cross-section. The two end surfaces 5 c,5 d make an angle with the axis 2, namely a right angle, and are flatand parallel to one another. The heat-exchange body 5 has first fluidconducting elements 21 and second fluid conducting elements 22alternately in succession around the axis 2. One of the first fluidconducting elements 21 is shown in part separately in FIGS. 8, 9 and 10.Each first fluid conducting element 21 has a first sheet metal element23 and two first edge strips 24 and 25. Sections of a second fluidconducting element 22 are also shown in FIGS. 6 and 7. Each second fluidconducting element 22 has a second sheet metal element 27 and two secondedge strips 28, 29. Gas-permeable, first and second intermediate layers31 and 32 are arranged between the successive sheet metal elements 23,27. The successive sheet metal elements, together with the gas-permeableintermediate layers 31, 32 arranged between them, bound first and secondfluid passages 33, 34 for the first fluid 15 and second fluid 16,respectively.

[0040] The first and second sheet metal elements 23, 27 are identicallyformed and have both identical shapes and identical dimensions. Thesheet metal elements 23, 27 have four edges opposite one another inpairs, are tetragonal in the flat, unbound state and form a right-angleparallelogram, namely a rectangle. The sheet metal elements 23, 27 areparallel to the axis 2 and, in a cross-section perpendicular to saidaxis, extend outward in an involute manner away from the axis 2. The twoshorter edges of each sheet metal element 23, 27 are straight, parallelto one another and to the axis and designated below as inner edge 23 a,27 a and outer edge 23 b, 27 b, respectively, the inner edges 23 a, 27 abeing present at the ends close to the axis and the outer edges 23 b, 27b being present at those ends of the sheet metal elements which arefurther away from the axis. The two longer edges of each sheet metalelement 23, 27 are curved and parallel to one another and are designatedbelow as side edges 23 c, 23 d and 27 c, 27 d, respectively. The sheetmetal elements 23, 27 have a dimension measured along the curved sideedges 23 c, 23 d, 27 c, 27 d, i.e. length, which is at least 2 times,preferably at least 2.5 times and, for example, at least or about 3times that dimension, i.e. width, of the sheet metal element which isparallel to the axis 2. The edge strips 24, 25, 28, 29 consist of ametallic material, namely of metal strips. The first edge strips 24, 25belonging to one of the first fluid conducting elements 21 are arrangedat the two side edges 23 c, 23 d of the first sheet metal element 23 ofthe relevant fluid conducting element and run along these curved sideedges. The second edge strips 28, 29 belonging to the second fluidconducting elements 22 are arranged at the inner edge 27 a and outeredge 27 b, respectively, of the second sheet metal element 27 of therelevant fluid conducting element and extend along these straight edges27 a, 27 b parallel to the axis 2. The various edge strips 24, 25, 28,29 are rectangular in cross-section and rest with their broaderlongitudinal surfaces on the sheet metal elements. The a [sic] narrowerlongitudinal surfaces of the edge strips are at least approximatelyflush with the sheet metal element edges along which they run. Thevarious edge strips 24, 25, 28, 29 extend at least approximately alongthe whole sheet metal element edges at which they are arranged. The edgestrips 24, 25 running along the curved side edges extend, for example,along the whole length of the side edges from the inner edge to theouter edge of the sheet metal elements. On the other hand, the edgestrips 28, 29 running along the straight edges 23 a, 23 b, 27 a, 27 bmay be, for example, slightly shorter than these edges. The ends of theedge strips 28, 29 are then slightly offset, for example about 2 to 4mm, away from the side edges of the sheet metal elements 23 and 27—asshown for the upper end of inner edge strips 28 in FIG. 12. The ends ofthe first and second edge strips should, however, preferably partlyoverlap at the corners of the sheet metal elements in a projectionparallel to the axis 2 and to the lateral surfaces 5 a, 5 b.

[0041] As will be explained in more detail, the passages 33, 34 and thefluid flows therein are at least in general in the longitudinaldirections of the sheet metal elements 23, 27 and thus parallel to theirside edges 23 c, 23 d, 27 c, 27 d. The side edges of the sheet metalelements and/or the edge strips 24, 25 running along the side edgestherefore also form the side edges of the passages 33, 34. The sheetmetal elements 23, 27, the edge strips 24, 25 running along their sideedges and the passages 33, 34 are substantially and at leastapproximately involute in a section perpendicular to the axis 2.However, their shapes may be flattened in the inner and/or outer edgeregions in which the edge strips 28, 29 are arranged and may deviate a[sic] slightly from the ideal involute shape. Apart from this, eachsheet metal element is free of angled and/or curved edge sections andalso free of protuberances and/or indentations, such as waves and/orribs and the like. Each sheet metal element is thus completely straightand smooth everywhere in the axial direction and substantially—i.e.apart from any stated small deviations at the inner edge and outeredge—at least approximately involute and smooth in cross-sections atright angles to the axis 2. Each sheet metal element is accordinglycontinuously and smoothly curved substantially everywhere [lacuna] asection at right angles to the axis 2 and in particular everywhere onthe same side so that the curvature has the same sign at all points ofthe sheet metal element.

[0042] In a section perpendicular to the axis 2, those edge sections ofthe sheet metal elements 23, 27 which form the inner edges 23 a, 27 a ofthe sheet metal elements are preferably more or less perpendicular tothat cylindrical, inner lateral surface 5 a of the heat-exchange body 5which is circular in cross-section. The sheet metal elements or thetangents to them can then make with the inner lateral surface 5 a anangle which is 65° to 115°, preferably 80° to 100° and, for example,about 85° to 95°. Accordingly, said tangents are also at leastapproximately radial to the axis 2. This ensures that the first fluidcan readily flow into the first passages during operation and that thenumber of sheet metal elements and passages distributed around the innerlateral surface 5 a has at least approximately the largest possiblevalue at a certain, predetermined diameter of the inner lateral surface5 a and when the adjacent sheet metal elements are certain distancesapart and at certain thicknesses of the sheet metal elements. Since thesheet metal elements are involute, the adjacent sheet metal elements arethe same distance apart everywhere from the inside to the outside. Inaddition, the dimension or length of a sheet metal element, measuredalong an involute, is of course greater than the difference between theradii of the two lateral surfaces 5 b and 5 a.

[0043] Each intermediate layer 31, 32 consists of a wire lattice which,for example, is approximately quadrilateral, namely a knitted wirefabric, which is shown particularly clearly in FIG. 9 and is denotedthere by 27. The knitted wire fabric 37 has a number of rows 37 a ofstitches comprising stitches 37 b. The adjacent stitches 37 b belongingto the same row 37 a of stitches are formed by cohesive wire sections.The wire sections belonging to successive rows 29 a of stitchesintersect one another at intersection points 37 c and form a sort ofnode there. Each row 37 a of stitches is in general transverse and atright angles to the side edges 23 c, 23 d, 27 c, 27 d of the sheet metalelements 23, 27 and hence also in general transverse and at right anglesto the longitudinal directions and side edges of the passages 33, 34.Each row of stitches, i.e. the straight line defined by those positionsof the stitches of this row of stitches which correspond to oneanother—for example of the summits of the stitches—can make, with theside edges 23 c, 23 d, 27 c, 27 d of the sheet metal elements 23, 27, anangle which is preferably 70° to 90° and better 80° to 100° or even 85°to 95° and as far as possible exactly 90°. The rows 37 a of stitcheswhich are adjacent to one another are intertwined.

[0044] The wire lattice or knitted wire fabric 37 is produced, duringits production, by knitting from a single continuous wire. During theknitting, for example, a loop is first formed. This is then cut open inits longitudinal direction and cut into approximately even pieces of thedesired sizes. Originally, all rows 37 a of stitches thus also consistof a continuous wire. If a knitted wire fabric is arranged between twosheet metal elements, each pair of successive rows 37 a of stitches isassociated at most at one end or even nowhere over a continuous wiresection.

[0045] The width of each first intermediate layer 31 is approximatelyequal to the width of the first passage 33 present between the edgestrips 24, 25. Each first intermediate layer furthermore extends atleast approximately from the inner edge 23 a to the outer edge 23 b ofthe coordinated first sheet metal element 23 and hence substantiallyover the whole length of the first passage 33. The width of each secondintermediate layer 32 is approximately equal to the whole width of thesheet metal elements 23, 27. Each second intermediate layer 32furthermore connects approximately to the edge strips 28 arranged at theinner edge 27 a of the coordinated sheet metal element 27 and extends inthe longitudinal direction of the sheet metal element 27 and of thesecond fluid passage 34 over the major part of the length of the fluidpassage 34 but not completely to the edge strip 29, so that a strip-likeregion of the second passage 34 remains free there, said strip-likeregion being parallel to the axis and to the outer edge 27 c.

[0046] The sheet metal elements 23, 27, the edge strips 24, 25, 28, 29and the knitted wire fabrics 37 consist, for example, of stainless,chromium-containing steel. The sheet metal elements have a thicknesswhich—depending on the other dimensions of the sheet metal elements—isat most 5 mm, expediently at most 1 mm, preferably at most 0.5 mm,usually even better at most 0.3 mm and, for example, about 0.2 mm. Thethickness of the wires forming the knitted wire fabrics is, for example,the same for all intermediate layers but could possibly be different forthe first and second intermediate layers and, likewise depending on thesize of the sheet metal elements, is at most 5 mm, expediently at most 1mm, preferably at most 0.8 mm and, for example, about 0.3 mm to about0.7 mm. The open area of the knitted wire fabrics 37 is preferably atleast 50% and, for example, about 60% to 90% of the total area occupiedby the knitted wire fabric.

[0047] The wires of the knitted wire fabrics 37 are preferably circularin cross-section. Each edge strip 24, 25, 28, 29 has a thickness whichis approximately equal to two times the diameter of the wires and/orpossibly a little larger than this diameter. Two sheet metal elements23, 27 adjacent to one another are adjacent to those two surfaces of theedge strips 24, 25 or 28, 29 present between them which face away fromone another. Furthermore, the two sheet metal elements are in each caseadjacent to one of the intersecting wire sections at the intersectionpoints 37 c of the wire lattice 37 present between said sheet metalelements. The edge strips 24, 25, 28, 29 and the intermediate layers 31,32 each consisting of a knitted wire fabric thus serve as spacer meansand keep the adjacent sheet metal elements the desired distance apart.In those regions of an intermediate space between two adjacent sheetmetal elements which are not occupied by intersection points 37 c, thisintermediate space is free. The intermediate layers 31, 32 arranged inthe intermediate spaces between the sheet metal elements are thus—asstated above—gas-permeable, so that the intermediate spaces form thefluid passages 33, 34.

[0048] The sheet metal elements 23, 27 adjacent to one another arefirmly connected to the edge strips 24, 25 or 28, 29 arranged betweenthem and thus also in pairs to one another. In the production of theheat-exchange body 5, for example, the first edge strips 24, 25 arefixed by a few spot weld joints denoted by 35 in FIGS. 8, 9 to thecoordinated, first sheet metal element 23 and the second edge strips 28,29 are fixed by a few spot weld joints to the coordinated, second sheetmetal element. The first and second fluid conducting elements 21 and 22are formed thereby. Furthermore, each of the intermediate layers 31, 32consisting of a knitted wire fabric is fastened at some points by spotweld joints to the coordinated sheet metal element 23 or 27,respectively. Each knitted wire fabric is thus fastened at most to asingle sheet metal element, so that the knitted wire fabrics support thesheet metal elements between which they are arranged but are not rigidlyconnected to one another. If the edge strips and knitted wire fabricswere fixed in the manner described to the coordinated sheet metalelement, the fluid conducting elements 21, 22 and intermediate layers31, 32 or knitted wire fabric can be assembled to give the heat-exchangebody and can be welded, for example, along the whole length of the edgestrips arranged between them to said edge strips and at these possiblyalso directly to one another. The sheet metal elements are then alsoconnected in pairs almost nondetachably and tightly to one another alongthe edge strips.

[0049] During welding of the sheet metal elements and edge strips, forexample, a pair of sheet metal elements 23, 27 can first be arranged oneon top of the other in a manner such that the inner edges 23 a, 27 a andthe outer edges 23 b, 27 b and the edge strips 28, 29 running alongthese edges are flush. The sheet metal elements and edge strips adjacentto one another can first be connected to the straight edge strips 28, 29and to one another along their inner edges 23 a, 27 a and outer edges 23b, 27 b by weld joints 38 or weld seams shown in FIGS. 11 and 12 and 33[sic]. If a plurality of, or all, sheet metal elements serving for theformation of the heat-exchange body are welded in pairs in this manner,these subunits each formed from a pair of sheet metal elements can beassembled to give a heat-exchange body and welded successively along theinvolute side edges 23 c, 23 d, 27 c, 27 d to the edge strips 24 and 25running along said side edges and via said edge strips to one another.Weld joints or weld seams are formed, one of which is shown in FIG. 12and denoted by 39. The sheet metal elements can then also possibly beconnected, at the ends or end surfaces of the curved edge strips 24, 25,to these edges strips and to one another by weld joints 39 a. The sheetmetal elements present in succession along the periphery of theheat-exchange body are then connected to one another alternately attheir inner and outer edges or at their side edges along the latter viathe edge strips arranged between the relevant edges. Weld joints whichrun continuously along the periphery of the inner edges and outer edgesof the end surfaces 5 c, 5 d around the axis 2 can be formed at the fourcorners of the sheet metal elements. On the other hand, the sheet metalelements 23, 27 together in pairs bounding a first passage 33 are freeof rigid connections at their inner edges 23 a, 27 a and at their outeredges 23 b, 27 b between the edge strips 24, 25 running along their sideedges. In an analogous manner, the sheet metal elements 23, 27 togetherin pairs bounding a second passage 34 are free of rigid connectionsbetween the sheet metal elements at their side edges 23 c, 23 d, 27 c,27 d between the edge strips 28, 29 arranged at their inner edges 23 a,27 a and outer edges 23 b, 27 b and running along said edges.

[0050] The heat-exchange body 5 can also be provided with at least oneretaining ring 40 encompassing its outer lateral surface and preferablywith two or more such rings, two retaining rings 40 a distance apart inthe axial direction being shown in FIG. 2 by way of example. Eachretaining ring has, for example, a metallic band consisting of stainlesssteel and possibly a clamping device for clamping the band so that, inthe assembled state, said band rests firmly against those outer edges ofthe sheet metal elements and/or edge strips which define the outerlateral surface 5 b of the heat-exchange body. The retaining rings canfurthermore be secured by additional retaining means to prevent axialdisplacements but should not be welded or otherwise rigidly connected tothe sheet metal elements or at any rate not to successive sheet metalelements.

[0051] The housing 3 has two annular retaining members 41 and 42 forholding the heat-exchange body 5 at its end surfaces 5 c, 5 d. Eachretaining member 41, 42 has an annular, metallic wall 43 or 44,respectively, which is angular in axial section and has two conicalparts or limbs inclined inward or outward away from its peak. A metallicfoil 45 or 46 which rests against the end surface 5 c or 5 d,respectively, of the body 5 is held on those edges of said wall whichface away from the peak. At least some of said edges of the walls 43, 44can furthermore be tightly welded to those points of the sheet metalelement edges and edge strips present next to them. For example, theinner edge of the lower wall 43 and the outer edge of the upper wall 44can be welded at the inner edge of the lower end surface 5 c and at theouter edge of the upper end surface 5 d of the heat-exchange body to thelatter. On the other hand, the outer edge of the lower wall 43 and theinner edge of the outer wall 44 are, for example, not welded to theheat-exchange body. The cavity bounded by the angular wall 43, 44 andthe foil 45 or 46 contains a heat-insulating, elastically deformableinsulation 47 or 48. This is heat-resistant up to very high temperaturesof, for example, at least about 1000° C. Each insulation 48 may consist,for example, of a preshaped, deformable body and contain, for example, afibre material and a binder. However, the insulation can also consist ofa filler material only loosely aggregated and capable of beingintroduced into the cavities of the walls. Each insulation 47, 48 restsagainst that side of the foil 45 or 46 which faces away from theheat-exchange body, and presses said foil against the end surface 5 c or5 d of the heat-exchange body. The walls 43, 44 and foils 45, 46consist, for example of stainless, chromium-containing steel. While thewalls 43, 44 are, for example, about 1 mm to 2 mm thick, the thicknessof the foils 45, 46 is at most 0.1 mm and, for example, 0.03 mm to 0.07mm. The foils are therefore fairly readily deformable and can fit snuglyagainst one another and against the end surfaces 5 c, 5 d. The foils 45,46 cover the major parts of the side edges of the sheet metal elements23, 27 and fluid passages 33, 34 and at least approximately tightly sealthe major parts of the second fluid passages 34 which are open at to[sic] the end surfaces 5 c, 5 d, at the side edges of said passages.

[0052] Each first fluid passage 33 has a first fluid inlet orifice 33 aand a first fluid outlet orifice 33 b for the first fluid 15. Eachsecond fluid passage 34 has a second fluid inlet orifice 34 a and asecond fluid outlet orifice 34 b for the second fluid. These orifices 33a, 33 b, 34 a, 34 b are all formed by slots between edge sections ofadjacent sheet metal elements 23, 27 bounding the relevant passage. Eachfirst inlet orifice 33 a is present between the inner edges 23 a, 27 aof two sheet metal element [sic] 23, 27. Each first outlet orifice 33 bis present between the outer edges 23 b, 27 b of two sheet metalelements 23, 27. The orifices 33 a, 33 b extend in the axial directionfrom an edge strip 24 to an edge strip 25. Each second inlet orifice 34a is present between sections of the side edges 23 c, 27 c of two sheetmetal elements 23, 27 in the proximity of the outer edges 23 b, 27 b ofthese sheet metal elements. Each second inlet orifice is approximatelyadjacent to the outer lateral surface 5 b and in fact runs away from anedge strip 29 inward to retaining member 41 and extends only over asection of the side edges 23 c, 27 c which is very much shorter than thetotal side edges. Each second outlet orifice 34 b is present betweensections of the side edges 23 d, 27 d of two sheet metal elements 23, 27in the proximity of the inner edges of the sheet metal elements. Eachsecond outlet orifice 34 b is approximately adjacent to the innerlateral surface 5 a and in fact runs away from an edge strip 28 outwardto the retaining member 42 and extends only along side edge sectionswhich are very much shorter than the total side edges 23 d, 27 d.

[0053] The first inlet orifices 33 a of the various first passagestogether define a first inlet region 5 e of the heat-exchange body 5.The first outlet orifices 33 b analogously define a first outlet region5 f. Furthermore, the second inlet orifices together and the secondoutlet orifices together define a second inlet region 5 g and a secondoutlet region 5 h, respectively. Each of these regions is annular and isin an area encompassing the axis 2. The first inlet region and the firstoutlet region are present at the inner lateral surface 5 a and at theouter lateral surface 5 b, respectively, and extend in the axialdirection over the major part of the lateral surfaces. The second inletregion 5 g and the second outlet region 5 h are present at and/or in oneof the two end surfaces 5 c or 5 d facing away from one another, butextend only over a small part thereof in the radial direction. The firstinlet region and the second outlet region are present at the inner edgesor in the proximity thereof, but these two regions are spatiallyseparated from one another. Similarly, the first outlet region and thesecond inlet region are also spatially separated from one another. Theinlet and outlet regions adjacent to one another in pairs are a distanceapart in the axial direction by an amount equal to the width of a firstedge strip 25 or 24 and along the involute side edges of the sheet metalelements by an amount equal to the width of a second edge strip 28 or29.

[0054] The inner lateral surface 5 a of the heat-exchange body 5encompasses a first, substantially cylindrical inlet chamber 51 which isadjacent to the first inlet region 5 e of the heat-exchange body. Thehousing 3 and/or the fluid conducting means 7 furthermore bound a firstoutlet chamber 52, a second inlet chamber 53 and a second outlet chamber54. The first inlet chamber 51 is closed, for example, at its end at thebottom in FIG. 2 by a hollow closure member 57 which has metallic walls58 and contains a heat insulation 59. The three chambers 52, 53, 54 areannular and, for example, bounded by metallic walls and are adjacent tothe first outlet region 5 f or the second inlet region 5 g or the secondoutlet region 5 h of the heat-exchange body 5. The fluid conductingmeans 7 have a conical inlet part 61 which connects the first fluidentrance 8 to the first inlet chamber 51, widens toward the first inletchamber 61 and is connected, namely welded, tightly to the heat-exchangebody approximately at the annular edge between the surfaces 5 a, 5 d ofsaid heat-exchange body. The fluid conducting means furthermore connectthe first outlet chamber 52 to the first fluid exit 9, the second fluidentrance 10 to the second inlet chamber 53 and the second outlet chamber54 to the second fluid exit 11, all these connections being tight.

[0055] The first and second sheet metal elements are completelyidentical apart from the edge strips fastened to them. As stated above,the sheet metal elements are completely straight everywhere in axialsections from one side edge to the other side edge and are substantiallycompletely involute everywhere from the inner edge to the outer edge insections transverse to the axis 2. They thus have no curved or anglededge sections. This contributes toward economical production of the heatexchanger.

[0056] The orifices 33 a, 33 b, 34 a, 34 b of the passages 33, 34connect the relevant passage between said edges of the sheet metalelements through to a space adjacent to these edges, in the vicinity ofthe heat-exchange body, namely to one of the chambers 51, 52, 53, 54.Those orifices of the heat-exchange body which serve for passing thefluids into the heat-exchange body and for discharging the fluids fromthe heat-exchange body are thus formed by constructionally simple means.The inlet and outlet orifices can be formed in particular without theheat-exchange body having to be provided with additional channels forthis purpose as is the case for various known heat exchangers. This alsocontributes toward economical producibility of the heat exchanger.

[0057] During the use of the heat exchanger 1, the first fluid 15consisting of exhaust gas has, in the first inlet chamber 51, an inlettemperature which is very much higher than the inlet temperature of thesecond fluid 16 consisting of air in the second inlet chamber 53. Thefirst fluid 15 is distributed in the inlet chamber 51 over the firstfluid inlet orifices 33 a and flows in these into the first fluidpassages 33, through these outward away from the axis 2 and then throughthe first fluid outlet orifices 33 b into the first outlet chamber 52.The first fluid flows in the heat-exchange body 5 in generalapproximately transversely to the axis 2 along the involute, firstpassages. The second fluid 16 flows from the second inlet chamber 53initially approximately parallel to the axis 2 through the second fluidinlet orifices 34 a into the second fluid passages 34, is distributed inthose initial sections of said passages which are free of knitted wirefabric over the axial dimension of the second passages, then flowsapproximately transversely to the axis 2 along the involute passagesfrom outside to inside toward the axis 2, is deflected again in theproximity of the inner ends of the passages into an approximately axialdirection and then flows through the second fluid outlet orifices 34 binto the second outlet chamber 54. Since the second inlet orifices 34 aand the second outlet orifices 34 b are located at the end surfaces 5 c,5 d which face away from one another, the second fluid 16 followsapproximately Z-shaped flow paths in the axial section shown in FIG. 5,but the major part of these flow paths are approximately transverse tothe axis 2 along involutes.

[0058] If the two fluids 15, 16 flow through the heat-exchange body indirections of flow which are for the most part opposite to one another,the originally much hotter, first fluid 15 consisting of exhaust gasreleases heat to the initially cold, second fluid 16 consisting of air.The first fluid is thus cooled along its flow paths from inside tooutside, while the second fluid is heated from outside to inside. Thetemperature of the heat-exchange body 5 thus decreases in an outwarddirection away from the axis so that the heat-exchange body has only alow temperature deviating at most slightly from ambient temperature atits relatively large, outer lateral surface 5 b. Since the sheet metalelements 23, 24 are very thin, they conduct only little heat to theoutside. The intermediate layers 31, 32 consisting of knitted wirefabrics 37 have only small material cross-sectional surfaces incomparison with the cross-sectional dimensions of the fluid passages 33,34 and accordingly result in only little heat conduction. Since the rows37 a of stitches of the wire lattices 37 are transverse to thelongitudinal direction of the passages, to the main directions of flowof fluids and to the temperature gradients in the heat-exchange body,the heat conducted by the wire lattices must moreover pass contactpoints of wire sections in order to pass from one row 37 a of stitchesto the next. In particular, the wire lattices therefore conduct onlyvery little heat away from the inside along the passages to the outside.The metallic foils 45, 46 present at the end surfaces 5 c, 5 d of theheat-exchange body are very thin and accordingly also result in onlylittle heat conduction. Furthermore, the foils in the axial directionare insulated by the insulations 47 and 48. For all these reasons, theheat exchanger releases only little heat to the environment so that avery large part of the heat of the hot exhaust gas or first fluid 15 canbe recovered.

[0059] The temperature of the first fluid 15 consisting of exhaust gasmay be, for example, 500° C. or about 1000° C. or possibly even morewhen passed into the heat exchanger. The various parts of theheat-exchange body 5 are therefore greatly expanded during operation inthe inner region of the heat-exchange body by the increase intemperature. The sheet metal elements 23, 27 adjacent to one another aresupported in a stable manner against one another by the edge strips 24,25, 28, 29 by those wire sections of the knitted wire fabrics 37 whichrest against one another at the intersection points 37 c and against thesheet metal elements, so that the diameters of the passages can bechanged approximately by the same amount for all passages even withlarge temperature changes. The wires of the knitted wire fabrics arecapable of relatively free deformation between the intersection points37 c, so that the temperature changes and temperature gradients do notcause any excessive stresses and any damage to the knitted wire fabricsand the sheet metal elements supported by them. The sheet metal elementspresent in succession around the axis 2 are—as described above—connectedto one another in each case at two edge strips 24, 25 or 28, 29 and areat least substantially unconnected at the other edges. Furthermore, thesheet metal elements are free of rigid connections in their main regionspresent between the edge strips. The described manner for connecting thesheet metal elements to give a heat-exchange body helps to ensure thatthe sheet metal elements are not damaged even by large temperaturechanges and temperature gradients. Furthermore, the formation of the tworetaining members 41, 42 engaging the end surfaces of the heat-exchangebody ensures that the sheet metal elements can also move slightlyperpendicularly to the axis 2 relative to the retaining members and thatthe latter can adapt to axial dimensional changes of the heat-exchangebody. As described, the length of the sheet metal elements and passagesmeasured along the curved side edges is at least 2 times and, forexample, at least or about 3 times the width, parallel to the axis, ofthe sheet metal elements and passages. This large ratio of length towidth makes the heat-exchange body readily deformable. For all thesereasons, the heat exchanger 1 is very solid and durable.

[0060] During tests, in particular numerous cold starts were alsocarried out, in which hot exhaust gas having temperatures of the orderof about 700° C. was abruptly fed to a cold heat exchanger. Although theheat exchanger is subjected to very high stresses during such coldstarts, no damage at all was found even after a large number of suchcold starts.

[0061] The internal diameter of a heat-exchange body may be, forexample, 250 mm to 1 m or more. Sheet metal elements adjacent to oneanother may then have, for example, spacings of about 1 mm, thethickness of the sheet metal elements being, for example, about 0.2 mm.The heat-exchange body can then have at least 500 or even at least 1000sheet metal elements and passages distributed around its axis. The largenumber of passages results in intensive heat exchange. The knitted wirefabrics moreover produce microturbulence in the fluids flowing throughthe passages. Consequently, the heat exchange between the two fluids isfurther improved.

[0062] The heat exchanger shown in parts in FIGS. 13 to 16 has one, andonly one, annular heat-exchange body 5, like the heat exchangerdescribed above. Said heat-exchange body is formed substantiallyidentically or similarly to the heat-exchange body described above andhas in particular an inner lateral surface 5 a, an outer lateral surface5 b and two end surfaces 5 c, 5 d facing away from one another. Onceagain, retaining members 41, 42 with walls 43, 44 for holding theheat-exchange body 5 are furthermore present. The lower retaining member41 is, however, formed in such a way that it completely covers the lowerend surface 5 c from the inner lateral surface 5 a to the outer lateralsurface 5 b and seals the second passages more or less air-tighteverywhere. In contrast, the upper retaining member 42 leaves both anannular region adjacent to the inner edge and an annular region adjacentto the outer edge free at the upper end surface 5 d. The second fluid 16consisting of cold air can flow into the heat-exchange body at theouter, uncovered annular region of the upper end surface 5 d and canflow out of the heat-exchange body again at the inner, uncovered annularregion of the same end surface 5 d. The second fluid 16 is thus passedalong an approximately U-shaped flow path into the heat-exchange body,through the latter and out of it again. Under certain circumstances,this may be advantageous for reasons relating to space. The first fluid15, on the other hand, is passed through the heat-exchange bodyanalogously to the heat exchanger described with reference to FIGS. 1 to12.

[0063] The heat exchanger according to FIGS. 13 to 16 furthermorediffers from the heat exchanger described above in that, instead of asingle foil 45 or 46, a plurality of metallic foils 75 or 76 distributedalong the periphery of the heat-exchange body and shown particularlyclearly in FIGS. 14 and 15 are present at each end surface 5 c, 5 d.Each involute sheet metal element and each fluid passage has, at eachend surface 5 c, 5 d, parts which are covered by at least two differentfoils 75 and 76. The two fluid passages 34 are once again open at theend surfaces 5 c, 5 d. The foils 75, 76 resting against the end surfaces5 c, 5 d overlap one another in such a way that the second fluid 16emerges at the overlaps of the foils, in each case in an outlet sectionof a foil, from the region which is covered by said foil and in whichthis foil is already covered by the foil in succession in the directionof flow of the second fluid.

[0064] In addition to a main section resting against the heat-exchangebody 5, each foil 75, 76 also has edge sections 75 a and 76 a,respectively. In the heat exchanger according to FIGS. 13 to 16, eachcavity bounded by one of the walls 43, 44 furthermore contains aninsulation 88 which is composed of two originally separated insulationparts 88 a and 88 b. The insulation part 88 a consists of a flat layerwhich rests against the main sections of the foils 75 and 76. The edgesections 75 a, 76 a of the foils are placed around the edges of theinsulation parts 88 a. The insulation parts 88 b rest against theinsulation parts 88 a and the surrounding edge sections 75 a, 76 a ofthe foils, thus clamp the surrounding edge sections and also serve forholding the foils firmly.

[0065]FIG. 16 also shows some weld joints, of which all those whichconnect the heat-exchange body 5 to parts of the housing and/or of theretaining members and/or fluid conducting means are denoted by 91.

[0066] Unless stated otherwise above, the heat exchanger according toFIGS. 13 to 16 may be formed identically or similarly to the heatexchanger according to FIGS. 1 to 12.

[0067] The heat exchanger 101 shown in FIGS. 17, 18 and 19 has an axis 2and a housing 103. The housing contains a first heat-exchange body 105.1and a second heat-exchange body 105.2. Furthermore, once again onlyschematically shown fluid conducting means 107 are present. FIG. 17 alsoshows parts of a gas turbine 112 whose housing is connected to thehousing 103 and the fluid conducting means 107 of the heat exchanger101. Furthermore, a first fluid 15 consisting of exhaust gas and asecond fluid 16 consisting of air are represented by arrows.

[0068] Each heat-exchange body 105.1, 105.2 has first and second fluidconducting elements alternately in succession around the axis 2. Thefirst fluid conducting elements are shown in FIG. 18 and are identicallyformed in the case of both heat-exchange bodies 105.1, 105.2 and alsoformed identically or similarly to the first fluid conducting elementsof the heat-exchange body 5 and, like these, are denoted by 21. On theother hand, the second fluid conducting elements of the twoheat-exchange bodies 105.1, 105.2 which elements are shown in FIG. 19,differ slightly from one another and are denoted by 122.1 and 122.2,respectively. Each first and second fluid conducting element has, asmain component, a first sheet metal element or second sheet metalelement, respectively. The sheet metal elements are all identicallyformed and dimensioned, also formed identically or similarly to sheetmetal elements 23, 27 of the heat-exchange body 5 and, like these,denoted by 23 and 27, respectively. The sheet metal elements of theheat-exchange body 105.1, 105.2 are provided, identically or similarlyto those of the heat-exchange body 5, with first edge strips 24, 25 andsecond edge strips 28, 29 and are connected to one another in pairs atthese.

[0069] First and second intermediate layers are arranged alternatelybetween those sheet metal elements of the heat-exchange bodies 105.1,105.2 which are present in succession around the axis. The firstintermediate layers of the two heat-exchange bodies, which layers areshown in FIG. 18, are all identically formed and arranged, furthermoreformed identically or similarly to those of the heat-exchange body 5and, like these, denoted by 31. Of the second intermediate layers shownin FIG. 19, those belonging to the first heat-exchange body 105.1 areformed and arranged identically or similarly to those of theheat-exchange body 5 and are denoted by 32. The second intermediatelayers of the second heat-exchange body 105.2 are denoted by 132.2 andare arranged slightly differently to the second intermediate layers 32of the first heat-exchange body 105. While each intermediate layer 32 isat least approximately adjacent to an edge strip 28 and is separatedfrom the edge strip 29 by an axial, strip-like, free intermediate space,each second intermediate layer 132 is at least approximately adjacent tothe edge strip 29 and is separated from the edge strip 28 by astrip-like, free intermediate space.

[0070] The housing 103 has retaining members 41 and 42 which are formedsimilarly to those of the housing 3 and, like these, are denoted by 41and 42, respectively. Each of these retaining members engages one of thetwo flat end surfaces 105.1 c and 105.2 d of the two heat-exchangebodies 105.1, 105.2, which end surfaces are furthest away from oneanother. An annular retaining member 143 is arranged between the twoheat-exchange bodies. Said retaining member has two short, cylindrical,metallic walls, namely an inner wall 144 and an outer wall 145, and twometallic foils 146, each of which rests against one of those endsurfaces 105.1 d and 105.2 c of the two heat-exchange bodies 105.1,105.2 which face one another. The interior encompassed by the walls 144,145 and the foils 146 contains a heat-insulating, elastically deformableinsulation 147. The retaining member 143 covers the major part of theend surfaces 105.1 d, 105.2 c of the two heat-exchange bodies but leavesone annular region each free on the inside and outside.

[0071] First and second fluid passages are present alternately betweenthe sheet metal elements present in succession around the axis. Thefirst fluid passages of the two heat-exchange bodies 105.1, 105.2, whichpassages are shown in FIG. 18, are all identically formed andidentically or similarly formed to those of the heat-exchange body 5and, like these, are denoted by 33.

[0072] The second fluid passages of the two heat-exchange bodies 105.1,105.2 are denoted by 134.1 and 134.2. respectively. The second passages134.1 of the first heat-exchange body 105 have a second fluid inletorifice 134.1 a and a second fluid outlet orifice 134.1 b, analogouslyto the second fluid passages 34 of the heat-exchange body 34, andadditionally have a fluid secondary outlet orifice 134.1 c. This ispresent at the end surface 105.1 d of the body 105 and is arranged inthe axial direction relative to the second inlet orifice 134.1 a.

[0073] Each second fluid passage 134.2 of the second heat-exchange body105.2 has a second fluid inlet orifice 134.2 a and a second fluid outletorifice 134.2 b. These two orifices are arranged similarly to thecorresponding orifices of the second passages of the heat-exchange body5. However, that section of the passage 134.2 which is flush with theinlet orifice 134.2 a in the axial direction also contains a section ofa second intermediate layer 132.2. Each second passage 134.2 of thesecond heat-exchange body 105.2 furthermore has a fluid secondary inletorifice 134.2 c. This is present in the proximity of the inner edges ofthe second sheet metal elements of the second heat-exchange body 105.2and lies in the end surface 105.2 c. Each secondary inlet orifice 134.2c is arranged opposite the second outlet orifice 134.2 b in the axialdirection and is connected to said outlet orifice by an axial strip-likeregion of the second passage 134.2 which is at least partly free, i.e.contains no section of the second intermediate layer 132.2.

[0074] The housing 103 and the fluid conducting means 107 are in partformed similarly to the housing 3 and the fluid conducting means 7 butalso bound an inner and an outer connecting passage 155 or 156. Theinner connecting passage 155 connects that annular, second outlet regionof the first heat-exchange body 105.1 which is defined by the secondoutlet orifices 134.1 b to that annular secondary inlet region of thesecond heat-exchange body 105.2 which is defined by the secondary inletorifices 134.2 c. The outer connecting passage 156 connects that annularsecondary outlet region of the first heat-exchange body 105.1 which isdefined by the secondary outlet orifices 134.1 c to that annular secondinlet region of the second heat-exchange body 105.2 which is defined bythe second inlet orifices 134.2 a.

[0075] When the heat exchanger 101 is used, originally hot exhaust gasflows as first fluid 15 from the inside to the outside through the firstpassages 33 of the two heat-exchange bodies 105.2 [sic] and 105.2. Thesecond fluid 16 consisting of originally colder air is passed throughthe second inlet orifices 134.1 a of the first heat-exchange body 105.1into its second passages 134.1 and then partly flows inward throughthese passages to the second outlet orifices 134.1 b and partly throughthe secondary outlet orifices 134.1 c and the outer connecting passage156 to the second inlet orifices 134.2 a of the second heat-exchangebody 105.2 and inward through its second passages 134.2 to its secondoutlet orifices 134.2 b. That part of the second fluid 16 which reachesthe second outlet orifices 134.1 b of the first heat-exchange body 105.1then flows through the inner connecting passage 155 to the secondaryinlet orifices 134.2 c of the second heat-exchange body 105.2 into theexit end region of the second passages 134.2 of the second heat-exchangebody 105.2. There, that part of the second fluid 16 which arrives fromthe first heat-exchange body 105.1 combines with that part of the secondfluid which has previously flowed from the outside to the inside throughthe whole second heat-exchange body. Those parts of the second fluid 16which have been combined with one another then flow through the secondoutlet orifices 134.2 b of the second heat-exchange body 105.2 and outof the latter.

[0076] Unless stated otherwise above, the heat exchanger 101 issimilarly formed and is used and operated similarly to the heatexchanger 1 and has similar properties to it.

[0077] The heat exchanger 201 shown in FIG. 20 has a housing 203. Thiscontains a plurality of, namely three, pairs of heat-exchange bodies.Each pair has a first heat-exchange body 205.1 and a secondheat-exchange body 205.2. The heat-exchange bodies 205.1 and 205.2 areformed similarly to the heat-exchange bodies 105.1 and 105.2 of the heatexchanger 101. The three pairs of heat-exchange bodies are offsetaxially relative to one another and are held a distance apart byretaining members 206 arranged between them. These retaining members 206are, for example, formed similarly to the retaining members 143 of theheat exchanger 101 but have larger axial dimensions. The fluidconducting means 207 of the heat exchanger 201 are formed for passing afirst fluid 15 and a second fluid 16 through the heat-exchange bodies205.1 and 205.2 belonging to the same pair, in a manner analogous tothat described for the heat exchanger 101 having only a single pair ofheat-exchange bodies.

[0078] The heat exchanger 301 shown in FIG. 21 has a plurality of,namely, for example, four annular heat-exchange bodies which are formedidentically or similarly to those of the heat exchanger described firstand are likewise denoted by 5. The annular heat-exchange bodies are adistance apart along the axis of the heat-exchanger and encompass acavity with an axial pipe 303. The cavity region present between theinner lateral surfaces of the heat-exchange bodies 5 and the pipe 303serves as a first inlet chamber 351 for the first fluid 15 and containssome conical baffle plates 305 which have an orifice in the centralregion and serve for distributing the first fluid over the variousheat-exchange bodies 5. The heat-exchange bodies 5 have, at each oftheir two end surfaces inlet orifices for the second fluid 16 in theproximity of the outer lateral surface and outlet orifices for thesecond fluid 16 in the proximity of the inner lateral surface. Thesecond fluid 16 flowing out of the uppermost heat-exchange body 5 at theupper end surface of said heat-exchange body passes into an annular,second outlet chamber 354. The remaining second fluid 16 flowing out ofthe heat-exchange bodies passes into annular, second outlet chambers 355which are connected to the pipe 303 by radial connecting channels 356arranged in a spoke-like manner. Said pipe is connected in the proximityof its upper end by a few connecting channels 357, for example inclinedrelative to the axis 2, to the second outlet chamber 354, from which thesecond fluid 16 can flow through an orifice of the housing of the heatexchanger and out of the latter. The connecting channels 356 arecomposed of half-shells. Furthermore, the other means for holding theheat-exchange bodies and for feeding the fluids to the heat-exchangebodies and for removing the fluids from the heat-exchange bodies arealso formed in a substantially modular manner so that the number ofidentically formed heat-exchange bodies can be changed in a simplemanner and adapted to intended fluid flow rates.

[0079] The heat exchangers can also be modified in other ways. Thus, inparticular features of the various heat exchangers described can becombined with one another. For example, in the case of all embodiments,the foils can be formed and held in a manner similar to that describedfor the heat exchanger according to FIGS. 13 to 16. In addition, theknitted wire fabric shown in FIGS. 5 and 19 and serving as secondintermediate layers 32 could extend over the whole lengths of the secondfluid passages 34, 134.1, 134.2—i.e. from the inner to the outer edgestrips. Furthermore, the wall 43 of the heat exchanger shown in FIGS. 1to 12 could possibly also be welded at its outer edge facing the lowerend surface 5 c—i.e. at the inner boundary of the second inlet region 5g—to the heat-exchange body 5 and/or the wall 44 could possibly also bewelded to the heat-exchange body 5 at its inner edge facing the upperend surface 5 d—i.e. at the outer boundary of the second outlet region 5h. In the case of the heat exchanger shown in FIGS. 13 to 16, the wall44 could possibly be welded in an analogous manner at its outer and/orits inner, the end surface 5 d [sic] of the heat exchanger 5 to thelatter. The weld joints between the sheet metal elements and edge stripsand between the heat-exchange bodies and those parts of the housingand/or fluid conducting means which are connected to said heat-exchangebodies can be replaced at least partly or completely with hard solderjoints and/or adhesive bonds. The first inlet orifices and the secondoutlet orifices of a heat-exchange body could, for example, be axiallyoffset relative to one another in the inner lateral surface of theheat-exchange body. The first outlet orifices and the second inletorifices of a heat-exchange body could analogously be axially offsetrelative to one another in the outer lateral surface of theheat-exchange body.

[0080] Furthermore, the sheet metal elements in the unwound, flat statecould form an oblique-angled parallelogram or have at least twononparallel edges opposite one another. In these cases, at least one ofthe lateral surfaces and/or end surfaces of the heat-exchange body wouldthen be conical. The sheet metal elements could possibly have even atleast one edge curved in the unwound, flat state of the sheet metalelements.

1. Heat exchanger comprising at least one heat-exchange body (5, 105.1,105.2, 205.1, 205.2) which is annular in cross-section, encompasses anaxis (2) and has sheet metal elements (23, 27, 127) which are present insuccession around said axis and together alternately bound firstpassages (33) for a first fluid (15) and second passages (34, 134.1,134.2) for a second fluid (16), each sheet metal element (23, 27, 127)having an inner edge (23 a, 27 a), an outer edge (23 b, 27 b) and twoside edges (23 c, 23 d, 27 c, 27 d) running from the inner edge (23 a,27 a) to the outer edge (23 b, 27 b), adjacent sheet metal elements (23,27, 127) having substantially constant distances from one another alongtheir side edges (23 c, 23 d, 27 c, 27 d), characterized in that eachsheet metal element (23, 27, 127) forms a quadrilateral, that metallicedge strips (24, 25) are arranged between the sheet metal elements (23,27, 127) together bounding a first passage (33) and run along the sideedges (23 c, 23 d, 27 c, 27 d) of said sheet metal elements and arefirmly and tightly connected to the relevant sheet metal elements (23,27, 127) and that metallic edge strips (28, 29) are arranged between thesheet metal elements (23, 27, 127) together bounding a second passage(34, 134.1, 134.2) and run along the inner edges (23 a, 27 a) and theouter edges (23 b, 27 b) of said sheet metal elements and are firmly andtightly connected to the relevant sheet metal elements (23, 27, 127). 2.Heat exchanger according to claim 1, characterized in that the inneredge (23 a, 27 a) and the outer edge (23 b, 27 b) of each sheet metalelement (23 a, 27 a) [sic] are straight and parallel to one another andthat the two side edges (23 c, 23 d, 27 c, 27 d) of each sheet metalelement (23, 27, 127) are parallel to one another and at right angles tothe inner edge (23 a, 27 a) and outer edge (23 b, 27 b).
 3. Heatexchanger according to claim 1 or 2, characterized in that the sheetmetal elements (23, 27, 127) are connected by welding or hard solderingor adhesive bonding to the edge strips (24, 25, 28, 29) and thus to oneanother.
 4. Heat exchanger according to any of claims 1 to 3,characterized in that the sheet metal elements (23, 27, 127) togetherbounding a first passage (33) are free, at their inner edges (23 a, 27a) and outer edges (23 b, 27 b), between the edge strips (24, 25)arranged at their side edges (23 c, 23 d, 27 c, 27 d), from rigidconnections between said edge strips.
 5. Heat exchanger according to anyof claims 1 to 4, characterized in that the two side edges (23 c, 23 d,27 c, 27 d) of the sheet metal elements (23, 27, 127) and the edgestrips (24, 25) running along them form end surfaces (5 c, 5 d) facingaway from one another, that the two passages (34, 134.1, 34.2) [sic]have inlet orifices (34 a, 134.1 a, 134.2 a) lying in one of the endsurfaces (5 c, 5 d) and outlet orifices (34 b, 134.1 b, 134.2 b) lyingin one of the end surfaces (5 c, 5 d), that the sheet metal elements(23, 27, 127) together bounding a second passage (34, 134.1, 134.2) arefree, at the side edges (23 c, 23 d, 27 c, 27 d) of these sheet metalelements (23, 27, 127), in at least one of the following regions, orrigid connections between them; a) between the edge strips (28, 29)arranged at their inner edges (23 a, 27 a) and outer edges (23 b, 27 b),b) between the inlet orifices (34 a, 134.1 a, 134.2 a) and the edgestrips (28) arranged at the inner edges (23 a, 27 a) and between theoutlet orifices (34 b, 134.1.b, 134.2 b) [sic] and the edge strips (29)arranged at the outer edges (23 b, 27 b), c) between the inlet orifices(34 a) and the outlet orifices (34 b).
 6. Heat exchanger according toany of claims 1 to 5, characterized in that each first passage (33) has,at the inner edges (23 a, 27 a) of the two sheet metal elements (23, 27,127) bounding it, at least one orifice (33 a) which connects the firstpassage (33) between these inner edges (23 a, 27 a) through to a spaceadjacent to said edges and that each first passage (33) has, at theouter edges (23 b, 27 b) of the two sheet metal elements (23, 27, 127)bounding it, at least one orifice (33 b) which connects the firstpassage (33) between these outer edges (23 b, 27 b) through to a spaceadjacent to said edges.
 7. Heat exchanger according to any of claims 1to 6, characterized in that each second passage (34, 134.1, 134.2) has,in the proximity of the outer edges (23 b, 27 b) and in the proximity ofthe inner edges (23 a, 27 a) of the two sheet metal elements (23, 27,127) bounding it, in each case at least one orifice (34 a, 34 b, 134.1a, 134.1 b) which connects the second passage (34, 134.1, 134.2) betweentwo opposite side edges (23 c, 23 d, 27 c, 27 d) of these sheet metalelements (23, 27, 127) through to a space adjacent to said edges. 8.Heat exchanger according to claim 7, characterized in that thoseorifices of the passages (33, 34, 134.1, 134.2) which are present at ornear the inner edges (23 a, 27 d) of the sheet metal elements (23, 27,127) serve as inlet orifices (33 a) of the first passages (3) or asoutlet orifices (34 b, 134.1 b, 134.2 b) of the second passages (34,134.1, 134.2), that those orifices of the passages (33, 34, 134.1,134.2) which are present at or near the outer edges (23 b, 27 b) serveas outlet orifices (33 b) of the first passages (33 a) or as inletsurfaces (34 a, 134.1 a, 134.1 b) of the second passages (34, 134.1,134.2), that fluid conducting means (7, 107, 207) are present in orderto convey the first fluid (15) to the inlet orifices (33 a) of the firstpassages (33) and away from the outlet orifices (33 b) of the firstpassages (33) and in order to convey the second fluid (16) to the inletorifices (34 a, 134.1 a, 134.1 b) of the second passages (34, 134.1,134.2) and away from the outlet orifices (34 b, 134.1 b, 134.2 b) of thesecond passages (34, 134.1, 134.2), and that the fluid conducting means(7, 107, 207) are formed in order to feed the first fluid to the inletorifices (33 a) of the first passages (33) at a temperature which ishigher than the temperature at which the second fluid (16) is fed to theinlet orifices (34 a, 134.1, 134.2) of the second passages (34, 134.1,134.2) so that the first fluid 825) [sic] releases heat to the secondfluid (16) and the or each heat-exchange body (5, 105.1, 105.2, 205.1,205.2) has a temperature generally decreasing outward away from the axis(2).
 9. Heat exchanger according to claim 8, characterized in that theinlet orifices (33 a) of the first passages (33) are arranged in a firstinlet region (5 e), the outlet orifices (33 b) of the first passages(33) are arranged in a first outlet region (5 f), the inlet orifices (34a, 134.1 a, 134.2 a) of the second passages (34, 134.1, 134.2) arearranged in a second inlet region (5 g) and the outlet orifices (34 b,134.1 b, 134.2 b) of the second passages (34, 134.1, 134.2) are arrangedin a second outlet region (5 h) of the or a heat-exchange body (5,105.1, 105.2, 205.1, 205.2) and that each inlet region (5 e, 5 g) andoutlet region (5 f, 5 h) runs in an annular manner around the axis (2).10. Heat exchanger according to any of claims 1 to 9, characterized inthat the inner edges (23 a, 27 a) of the sheet metal elements (23, 27,127) and the edge strips (28) arranged at the inner edges (23 a, 27 a)define an inner lateral surface (5 a), that the sheet metal elements(23, 27, 127) adjacent to one another are at least approximately aconstant distance apart from their inner edges (23 a, 27 a) to theirouter edges (23 b, 27 b) and that those sections of the sheet metalelements (23, 27, 127) which are adjacent to the inner edges (23 a, 27a) have, in a cross-section at right angles to the axis (2), a tangentwhich makes with the inner lateral surface (5 a) an angle which is 65°to 115° and, for example, 80° to 100°, the sheet metal elements (23, 27,127) being preferably substantially involute in a section at rightangles to the axis (2).
 11. Heat exchanger according to any of claims 1to 10, characterized in that the side edges (23 c, 23 d, 27 c, 27 d) ofthe sheet metal elements (23, 27, 127) and the edge strips (24, 25)arranged at the side edges (23 c, 23 d, 27 c, 27 d) define two endsurfaces (5 c, 5 d) of the or each heat-exchange body (5, 105.1, 105.2,205.1, 205.2) and that the inlet orifices (34 a, 134.1 a, 134.2 a) andthe outlet orifices (34 b, 134.1 b, 134.2 b) of the second passages (34,134.1, 134.2) are arranged at end surfaces (5 c, 5 d) facing away fromone another.
 12. Heat exchanger according to claim 1, characterized inthat it has at least one pair of heat-exchange bodies, comprising afirst heat-exchange body (105.1, 205.1) and a second heat-exchange body(105.2, 205.2), that each heat-exchange body (105.1, 105.2, 205.1,205.2) has an inner and an outer lateral surface, that the secondpassages (134.1) having the inlet orifices (134.1 a) arranged in an endsurface (105.1 c) of the first heat-exchange body (105.1, 205.1) havesecondary outlet orifices (134.1 a) arranged in the other end surface(105.1 d) in the proximity of the outer lateral surfaces of the firstheat-exchange body (105.1, 205.1), that the second passages (134.2)having the outlet orifices (134.2 b) of the second heat-exchange body(105.2, 205.2) which are arranged in an end surface (105.2 c) havesecondary inlet orifices (134.2 c) arranged in the other end surface(105.2 c) in the proximity of the inner lateral surface of the secondheat-exchange body (105.2, 205.2) and that the fluid conducting means(107, 207) are formed in order to convey the second fluid (16) into thefirst heat-exchange body (105.1) at those inlet orifices (134.1 a) ofthe second passages (134.1) which are arranged in an end surface (105.1c) and then to convey part of this fluid (16) from the secondary outletorifices (134.1 c) of the first heat-exchange body (105.1) to thosesecond inlet orifices (134.2 a) of the second heat-exchange body (105.2,205.1) which are arranged in an end surface (105.2 c) and in order toconvey second fluid (16) which flows out of the second outlet orifices(134.1 b) arranged in an end surface (105.1 b) of the firstheat-exchange body (105.1, 205.1) to the secondary inlet orifices (134.2c) of the second heat-exchange body (105.2, 205.2).
 13. Heat exchanger,in particular according to any of claims 1 to 12, comprising at leastone heat-exchange body (5, 105, 105.2, 205.1, 205.2) having successivesheet metal elements (23, 27, 127) which alternately bound passages (33,34, 134.1, 134.2) for a first fluid (15) and a second fluid (16) andbetween which gas-permeable intermediate layers (31, 32, 132.2) arearranged, each sheet metal element (23, 27, 127) having two side edges(23 c, 23 d, 27 c, 27 d) facing away from one another, characterized inthat the side edges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements(23, 27, 127) belonging to the same heat-exchange body (5, 105.1, 105.2,205.1, 205.2) and/or edge strips (24, 25) arranged at these side edges(23 c, 23 d, 27 c, 27 d) together define two end surfaces (5 c, 5 d,105.1 c, 105.1 d, 105.2 c, 105.2 d) of the heat-exchange body (5, 105.1,105.2, 205.1, 205.2), that at least one metallic foil (45, 46, 75, 76,146) rests against the side edges (23 c, 23 d, 27 c, 27 d) of the sheetmetal elements (23, 27, 127) at each end surface (5 c, 5 d, 105.1 c,105.1 d, 105.2 c, 105.2 d) and that a heat insulation (47, 48, 88, 157)is arranged on that side of each foil (45, 46, 75, 76, 146) which facesaway from the sheet metal elements (23, 27, 127).
 14. Heat exchangeraccording to claim 13, characterized in that each foil (45, 46, 75, 76,146) is at most 0.1 mm and, for example, 0.03 mm to 0.07 mm thick. 15.Heat exchanger according to claim 12 or 13, characterized in that theinsulation (47, 48, 88, 147) presses the foil (45, 46, 75, 76, 146)against the sheet metal elements (23, 27, 127), the insulation (47, 48,88, 147) being, for example, elastically deformable.
 16. Heat exchangeraccording to any of claims 13 to 15, characterized in that at least twofoils (75, 76) which have sections which are adjacent to the endsurfaces (5 c, 5 d, 105.1 c, 105.1 d, 105.2 c, 105.2 d) and overlap oneanother are present at each end surface (5 c, 5 d, 105.1 c, 105.1 d,105.2 c, 105.2 d) of the or each heat-exchange body (5, 105.1, 105.2,205.1, 205.2).
 17. Heat exchanger, in particular according to any ofclaims 1 to 16, comprising at least one heat-exchange body (5, 105.1,105.2, 205.1, 205.2) which is annular in cross-section, encompasses anaxis (2) and has sheet metal elements (23, 27, 127) which are present insuccession around said axis and together alternately bound firstpassages (33) for a first fluid (15) and second passages (34, 134.1,134.2) for a second fluid (16), each sheet metal element (23, 27, 127)having an inner edge (23 a, 27 a), an outer edge (23 b, 27 b) and twoside edges (23 c, 23 d, 27 c, 27 d) running from the inner edge (23 a,27 a) to the outer edge (23 b, 27 b), adjacent sheet metal elements (23,27, 127) having substantially constant distances from one another alongtheir side edges (23 c, 23 d, 27 c, 27 d), the passages (33, 34, 134.1,134.2) extending between orifices (33 a, 134.1 b, 134.2 b, 134.2 c) inthe proximity of the inner edges (23 a, 27 a) and orifices (33 b, 34 a,134.1 a, 134.1 c, 134.2 a) in the proximity of the outer edges (23 b, 27b), characterized in that the sheet metal elements (23, 27, 127) have adimension, measured along their side edges (23 c, 23 d, 27 c, 27 d),which is at least two times a dimension of the sheet metal elements (23,27, 127) which is measured along the axis (2).
 18. Heat exchangeraccording to claim 17, characterized in that it has at least twoheat-exchange bodies (105.1, 105.2, 205.1, 205.2) a distance apart alongthe axis (2).
 19. Heat exchanger according to claim 17 or 18,characterized in that the distance between adjacent sheet metal elements(23, 27, 127) is at most 10 mm and preferably at most 2 mm.
 20. Heatexchanger according to any of claims 17 to 19, characterized in that theor each heat-exchange body (5, 105, 105.2, 205.1, 205.2) has at least500 passages (33, 34, 134.1, 134.2) distributed around the axis (2). 21.Heat exchanger, in particular according to any of claims 1 to 20,comprising at least one heat-exchange body (5, 105, 105.2, 205.1, 205.2)having successive sheet metal elements (23, 27, 127) which alternatelybound passages (33, 34, 134.1, 134.2) for a first fluid (15) and asecond fluid (16) and between which gas-permeable intermediate layers(31, 32, 132.2) are arranged, each sheet metal element (23, 27, 127)having two side edges (23 c, 23 d, 27 c, 27 d) facing away from oneanother and parallel to one another, and at least substantial parts ofthe passages (33, 34, 134.1, 134.2) running along the side edges (23 c,23 d, 27 c, 27 d) characterized in that each intermediate layer (31, 32,132.2) consists of a knitted wire fabric (37) which has rows (37 a) ofstitches comprising stitches (37 b) which are adjacent to one anotherand are formed from cohesive wire sections, and that these rows (37 a)of stitches are generally approximately at right angles to the sideedges (23 c, 23 d, 27 c, 27 d) of the sheet metal elements (23, 27,127).
 22. Heat exchanger according to claim 21, characterized in thateach knitted wire fabric (37) is fastened at points to one, and onlyone, sheet metal element (23, 27) adjacent to it, for example eachknitted wire fabric (37) being fastened by a few spot welds to saidsheet metal element (23, 27) adjacent to it.
 23. Heat exchangeraccording to claim 21 or 22, characterized in that two rows (37 a) ofstitches present in succession along the side edges (23 c, 23 d, 27 c,27 d) have at most a single cohesive wire section, apart from theinterlinked stitches (37 b).
 24. Heat exchanger according to any ofclaims 21 to 23, characterized in that the or each heat-exchange body(5, 105.1, 105.2, 205.1, 205.2) encompasses an axis (2) and is annularin a cross-section at right angles to said axis, that each sheet metalelement (23, 27, 127) has an inner edge (23 a, 27 a) and an outer edge(23 b, 27 b), that the side edges (23 c, 23 d, 27 c, 27 d) run from theinner edge (23 a, 27 a) to the outer edge (23 b, 27 b) and make an anglewith the axis (2), that sheet metal elements (23, 27, 127) adjacent toone another have substantially constant distances from one another alongthe whole lengths of their side edges (23 c, 23 d, 27 c, 27 d) and thatthe passages (33, 34, 134.1, 134.2) are closed along at least thelargest parts of the side edges (23 c, 23 d, 27 c, 27 d) of the sheetmetal elements (23, 27, 127).
 25. Heat exchanger according to claim 24,characterized in that a first passage (33) for the first fluid (15) anda second passage (34, 134.1, 134.2) for the second fluid (16) arepresent alternately in succession around the axis (2), that edge strips(24, 25) running at each first passage (33) along the side edges (23 c,23 d, 27 c, 27 d) of the sheet metal elements (23, 27, 127) boundingthis first passage (33) are arranged between the two sheet metalelements (23, 27, 127) and are connected firmly and tightly to thelatter and that edge strips (28, 29) running at each second passage (34,134.1, 134.2) along the inner edges (23 a, 27 a) and along the outeredges (23 b, 27 b) of the sheet metal elements (23, 27, 127) boundingthis second passage (34, 134.1, 134.2) are arranged between the sheetmetal elements (23, 27, 127) and are firmly and tightly connected to thelatter.
 26. Heat exchanger according to claim 24 or 25, characterized inthat the sheet metal elements (23, 27, 127) adjacent to one another areeverywhere at least approximately a constant distance apart, apart fromany edge strips (24, 25, 28, 29) connected at edges (23 a, 23 b, 23 c,23 d, 27 a, 27 b, 27 c, 27 d) of said sheet metal elements to said sheetmetal elements and arranged between adjacent sheet metal elements (23,27, 127), are completely smooth, straight and parallel to one another inthe axial direction and are curved completely parallel to one anotherand smooth and, for example, substantially involute in sectionsperpendicular to the axis (2), so that the sheet metal elements (23, 27,127) are free of protuberances and indentations, such as, for example,waves and/or ribs and the like, and of angled and/or curved edgesections.
 27. Heat exchanger according to any of claims 21 to 26,characterized in that each sheet metal element (23, 27, 127) has athickness which is at most 5 mm, expediently at most 1 mm, preferably atmost 0.5 mm and, for example, at most 0.3 mm, and that the knitted wirefabrics (37) consist of wires whose thickness is at most 5 mm,expediently at most 1 mm, preferably at most 0.8 mm and, for example,0.3 mm to 0.7 mm, the sheet metal elements (23, 27, 127) and knittedwire fabrics (37) preferably consisting of stainless steel.